1. Field of the Invention
This invention relates to nano powders/particulates and micron powders/particulates and mixtures thereof.
2. Description of the Related Art
Nano powders/particulates (<100 nm size) produced by various synthesis methods such as gas condensation, sol gel, flame synthesis and other methods typically are in the agglomerate form. These agglomerates are very difficult to handle for using them in powder metallurgy processing operations such as filling into dies and compacting into uniform net shape.
Attempts to break up such nano powder agglomerates using conventional blending processes, ultrasonic mixing or simple milling proved not highly successful.
In the technology of powder metallurgy, different types of powders are blended together, sometimes with the inclusion of lubricants. Different types of blending devices are used, one type being the well-known V-blender.
A problem has been observed in attempting to mix together specific sizes of powders, such as nano-sized powders with micron-sized powders. When one mixes two such powders in the conventional manner and then attempts to compact and sinter the mixture, it is found that the nano powders tend to clump together and form separated islands within the matrix of the micron-powders. A highly homogeneous mixture is not attained.
FIG. 1 is a photo-micrograph of such a mixture. The bright areas indicate the metallic phase. The dark areas indicate the ceramic material. The reference dimension is 200 micro-meters or 200 microns.
The lack of homogeneity causes the physical and chemical properties to be non-uniform throughout the bulk of the mixture of powders. This non-uniformity carries over to the sintered product, which will also exhibit variance in properties throughout. The variance is not desired in many situations.
Sometimes milling is used to produce fine powders, by pulverizing coarser particles into a finer size. Milling can also be used to achieve mechanical alloying of two different powders.
In the ball milling process generally, one or more powders are placed into a milling jar, together with balls (or suitable grinding media) of hard material. The milling jar is rotated, to cause the contents to tumble. During the tumbling, the hard balls fracture the powders into finer sizes. If the milling is done at appropriate speeds for long duration, such as more than 10 hours, freshly formed surfaces of different materials react and mechanical alloying takes place.
What is needed is a system and process that overcomes one or more of the problems of the prior art.